Filter

ABSTRACT

A flat bed filter in which a filter medium in strip form is supported on an endless conveyor and supports a pool of contaminated liquid to be filtered. The conveyor is periodically advanced to provide fresh filter medium for filtering the contaminated liquid. The underside of the conveyor communicates with an evacuated compartment which is separated into separate chambers by a transverse partition. The transverse partition is in sealing engagement with the underside of the conveyor that advances the filter medium, and a means is provided for maintaining the chamber nearest the supply of filter medium at a higher pressure than the adjacent chamber in order to reduce the flow rate of contaminated liquid through the portion of filter medium initially exposed to the pool of liquid to be filtered.

United States Patent Lee et a].

[ Sept. 12, 1972 [54] FILTER FOREIGN PATENTS OR APPLICATIONS France..2l0/387 Primary Examiner-John Adee Attorney-Curtis, Morris & Safford[5 7] ABSTRACT A flat bed filter in which a filter medium in strip formis supported on an endless conveyor and supports a pool of contaminatedliquid to be filtered. The conveyor is periodically advanced to providefresh filter medium for filtering the contaminated liquid. The undersideof the conveyor communicates with an evacuated compartment which isseparated into separate chambers by a transverse partition. Thetransverse partition is in sealing engagement with the underside of theconveyor that advances the filter medium, and a means is provided formaintaining the chamber nearest the supply of filter medium at a higherpressure than the adjacent chamber in order to reduce the flow rate ofcontaminated liquid through the portion of filter medium initiallyexposed to the pool of liquid to be filtered.

6 Claims, 2 Drawing Figures PATENTEDSEP 1 2 I972 wuofm HY V ATTORNEYSFILTER The present invention relates to filters and more particularly toa flat bed filter which incorporates apparatus for reducing the amountof contaminated liquid that initially flows through the fresh filtermedium and thereby reduces the amount of such contaminated liquid thatmust be recirculated for further filtration. The invention is especiallyuseful in connection with the filtration of machine tool coolants andwill be illustratively described in relation to this application.However, as the description proceeds, it will be apparent that theapparatus of the invention can also be used for filtering other types ofcontaminated liquids.

Conventional flat bed filters commonly comprise .a liquid permeable,endless conveyor, such as an interlocking wire mesh belt, which isdriven intermittently in a fixed path around an evacuated compartment inwhich filtered liquid is collected. A sheet of filter medium, such asporous paper or cloth, is fed onto the upper side of the conveyor formovement therewith and the conveyor is so guided as to form a pool ofliquid to be filtered on the top of the filter medium.

Contaminated liquid, e.g., a machine tool cutting fluid or coolant, isfed continuously to the pool of liquid, and filtrate is continuouslyremoved from the evacuated compartment. As filtration proceeds, a'cakeis built up on the filter medium and the resultant increase in pressuredrop across the filter cake and medium causes the pressure within theevacuated compartment to decrease. The evacuated compartment is providedwith a pressure-responsive switch which when,

the pressure drops below a predetermined value actuates a drivingmechanism to cause the conveyor to move a section of fresh filter mediuminto the pool of liquid. The consequent increase in pressure within theevacuated compartment actuates the pressure-responsive switch to causethe conveyor to be stopped when a predetermined amount of fresh filtermedium has been advanced into the pool.

Since the fresh filter medium entering the pool has no filter cakethereon, the filtration rate therethrough is relatively high andaccordingly a certain amount of the contaminant passes through thisportion of the filter medium. Since this incompletely filtered liquidcannot be directly returned to the work area, it is customary to providea separate section of the evacuated compartment for collecting theincompletely filtered liquid so that it can be recycled for furtherfiltration.

Filters of the type described above are subject to the disadvantage thatin many cases, especially where the evacuated compartment is operated ata relatively high vacuum, an excessively high flow rate of liquidthrough the fresh filter medium into the recirculation section of theevacuated compartment is obtained until such time as the fresh filtermedium becomes coated with a filter cake that reduces the flow ratetherethrough. The initial flow rate of incompletely filtered liquid thatmust be circulated is often so high as to seriously impair the capacityof the filter. Thus this high rate of recirculation is undesirable andcontributes to an inefficient performance of the filtration unit.

It is accordingly an object of the present invention to provide a flatbed filter wherein the volume of incompletely filtered liquid that mustbe recycled is substantially reduced. It is another object of theinvention to provide a flat bed filter which includes means for reducingthe flow rate of contaminated liquid through the fresh filter medium atthe end of the pool of liquid to be filtered at which the filter mediumenters the pool. It is a further object of the invention to providemeans for selectively adjusting the flow rate of incompletely filteredliquid through the fresh filter medium in relation to the overallfiltration rate. It is still another object of the invention to providemeans for establishing a desired pre-coat of filter cake on the freshfilter medium while minimizing the amount of contaminated liquid thatflows therethrough. Other objects of the invention will be in partobvious and in part pointed out hereafter.

The objects and advantages of the invention may be achieved, in general,by providing in a filter of the general type described above a separaterecirculation chamber communicating with the portion of the conveyorthat supports the fresh filter medium and effectively sealed from themain vacuum chamber of the filter. This separate chamber has selectivelyadjustable means associated therewith for varying the pressure thereinindependently of the pressure in the main vacuum chamber. Theconstruction is such that a pressure can be maintained in therecirculation chamber which, although it may be at atmospheric pressureor below atmospheric pressure, is substantially higher than the pressurein the main vacuum chamber. Thus the pressure drop through the freshfilter medium at the end of the pool of contaminated liquid where thefilter medium enters the pool is reduced and flow of contaminated liquidtherethrough is consequently decreased.

In order to point out more fully the nature of the present invention,reference will now be made to the accompanying drawings which illustrateapparatus incorporating a preferred embodiment of the invention. It isto be expressly understood, however, that the description of thispreferred embodiment is intended to be for purposes of illustration onlyand not to define the limits of the invention, reference being had forthis purpose to the appended claims:

In the drawings:

FIG. 1 is a semi-diagrammatic side view of a flat bed filter, largely insection and showing the general arrangement of conveyor, filter medium,main vacuum chamber and recirculation chamber; and

FIG. 2 is an enlarged partial horizontal section taken on the line 2-2of FIG. 1 and showing mean for maintaining independent pressures in therecirculation chamber and the main vacuum chamber.

Referring now to the drawings and particularly to FIG. 1, the apparatusthere shown comprises the filter proper generally designated by thenumeral 10 and beneath the filter a liquid accumulator tank generallydesignated by the numeral 12. The filter 10 comprises a tank 14 havingend walls 16 and 18, side walls 20 (only one of which is shown) andbottom 22. Within tank 14 there is a fluid permeable, endless conveyor24 mounted on four pairs of sprockets 26, 28, 30 and 32, only onesprocket of each pair being shown in the drawing. The sprockets aresecured to shafts 26a, 28a, 30a and 32a which in turn are rotatablymounted in the side walls 20 of tank 14. The conveyor is driven throughshaft 26a by a motor 34 and chain drive 36 and is periodically advancedcounterclockwise in a manner more fully described hereafter.

The right-hand end of the upper course of conveyor 24 is supported by adownwardly sloping guide plate 38 and the left-hand end of the uppercourse of the conveyor is supported by an upwardly sloping guide plate40. The upper course of conveyor 24 in turn supports a strip of filtermedium 42, which may be, for example, paper or cloth, and which issupplied to the conveyor from a roll 44 rotatably mounted at theright-hand end of tank 14. The upper course of conveyor 24 and theportion of filter medium 42 supported thereon cooperate with tank sidesto define a shallow depression adapted to contain a pool 46 of theliquid to be filtered, e.g., a machine tool coolant. Conventional liquidsealing means (not shown) are'provided at the sides of the tank toprevent the liquid of pool 46 from by-passing the filter medium 42.

Located within the conveyor 24 there is a vacuum compartment 48 which isdefined by guide plate 38, right end wall 50, bottom wall 52, left endwall 54,

guide plate 40 and the adjacent portions of side walls 20 of tank 14.The compartment 48 is divided by a vertical transverse partition I 56into a main vacuum chamber 58 and recirculating chamber 60. The parti'tion 56 efi'ectively provides a seal between the chambers 58 and 60 topermit a pressure difference to be established between the two chambersas more fully described below. Connected to the upper left-hand portionof chamber 58 there is a conduit 62 leading to a vacuum pump 64 by meansof which the chamber is evacuated.

The portion of conveyor 24 between the ends of guide plates 38 and 40 isexposed to the interior of chamber 58, and thus the reduced pressure inchamber 58 tends to promote the flow of coolant through the filtermedium and conveyor, and filtered coolant accumulates in chamber 58. Inlike manner, guide plate 38 is provided with a transverse slot 66through which filtered coolant can flow into chamber 60.

As pointed out above, the conveyor 24 is periodically advancedcounterclockwise to bring fresh filter medium into contact with thecoolant at the right-hand end of the pool 46 and to remove spent filtermedium from the left-hand end of the pool. This periodic movement isinitiated and stopped by a switch (not shown) which is responsive to thepressure in chamber 58 and controls the operation of motor 34. As thefiltration operation proceeds,.a filter cake 68 is built up on filtermedium 42, thereby increasing the pressure drop between pool 46 and theinterior of chamber 58. Then the pressure in chamber 58 reaches apredetermined relatively low value, the pressure-responsive switch isactivated to start motor 34. As fresh filter medium is carried into theright-hand end of pool 46, the pressure in chamber 58 rises and when itreaches a predetermined relatively higher value, the pressure switch isagain activated to stop motor'34.

As pointed out above, since the fresh filter medium has no filtercoating, the coolant passing therethrough and flowing through slot 66into chamber 60 is incompletely clarified and must therefore berecirculated. This incomplete filtration continues until a sufficientcoat of filter cake has been built up on the filter medium. Thepressure-responsive switch is so adjusted in relation to the supply offluid to be filtered that an adequate precoat is built upon the filtermedium before it becomes exposed to the vacuum in chamber 58, and

thus only completely clarified coolant enters the latter chamber.

At the left end of the conveyor 24 the spent filter medium 42 andassociated filter cake 68 are separated from the conveyor and moveddownwardly to a separator member 70 which removes the filter cake fromthe filter medium and guides it to a container 72. The filter mediumfrom which the cake has been removed is collected in a container 74.

Referring now to the lower portion of FIG. 1, the accumulator tank 12 isprovided with an internal transverse dam 76 which divides it into adirty coolant chamber 78 containing a body of dirty coolant to befiltered and a clean filtrate chamber 80 containing a body of cleanfiltrate. As shown in the drawing, clean filtrate from chamber 80 canflow over dam 76 into chamber 78. Dirty coolant from the work areaenters chamber 78 through an inlet 82. Dirty coolant is withdrawn fromchamber 78 through a conduit 84 containing a valve 86 and is deliveredto the suction of a pump 88 driven by a motor 90. The pump 88 pumps thedirty coolant through a conduit 92 to a distributor 94 which distributesthe coolant to be filtered through openings 95 to the pool 46. To limitthe height of the liquid in pool 46, an overflow slot 96 is providedthrough which liquid from the pool can flow to a conduit 97 that extendsdownwardly into dirty coolant chamber 78.

Clean filtrate from the main vacuum chamber 58 flows through conduit 98to the chamber 80 and is withdrawn'therefrom through a conduit 100containing a valve 102. The conduit 100 delivers the clean filtrate tothe suction of a pump 104 driven by a motor 106 and the filtrate ispumped by pump 104 through a conduit 108 back to the work area forreuse.

Incompletely filtered coolant accumulating in the recirculation chamber60 flows through a conduit 110 containing a valve 112 to the dirtycoolant chamber 78 and is recirculated for further filtration along withthe dirty coolant entering chamber 78 through inlet 82.

As indicated above, if the portion of the conveyor 24 supporting thefresh filter medium and the portion of the conveyor having a filter cakebuilt up thereon are subjected to the same relatively low pressure, thevolume of incompletely filtered coolant passing through the filtermedium and requiring recirculation and refiltering constitutes anexcessively high proportion of the dirty coolant coming from the workarea and thus significantly reduces the capacity of the filter. Inaccordance with the present invention the flow rate of this incompletelyfiltered coolant is reduced by providing the recirculation chamber 60which is effectively sealed from the main vacuum chamber 58 by thepartition 56 and also providing means for establishing within thechamber 60 a pressure that is higher than the pressure in main vacuumchamber 58, thereby reducing the flow rate of the incompletely filteredcoolant into chamber 60. This means for establishing a pressuredifference between chambers 58 and 60 is most clearly shown in FIG. 2 ofthe drawing.

Referring to FIG. 2, as well as to FIG. 1, the chamber 60 is connectedthrough side wall 20 of tank 14 with a branch conduit 114 which in turnis connected to a main conduit 116 having a valve 118 therein and an end120 open to he atmosphere. Conduit 116 is also connected to a branchconduit 122 which contains a valve 124 and communicates through wall oftank 14 with the interior of main vacuum chamber 58. It is evident thatwhen valve 118 is closed and valve 124 is open,'chamber 60 will bemaintained at the same pressure as chamber 58; whereas when valve 118 isopen and valve 124 closed, chamber 60 will be maintained at atmosphericpressure. For intermediate settings of valves 118 and 124 the pressurein chamber 60 will have a value between atmospheric pressure and therelatively low pressure in chamber 58. Thus the valves 118 and 124 withtheir associated conduits 114, 116 and 122 provide a means whereby thepressure in chamber 60 can be selectively maintained at any desiredpressure between atmospheric pressure and the pressure in chamber 58,and the flow rate of incompletely filtered coolant that must berecirculated can be maintained at a desired value.

It is, of course, to be understood that the foregoing description of apreferred embodiment of the invention is intended to be illustrativeonly. For example, since the liquid level of pool 46 tends to rise asfilter cake builds up on the filter medium and tends to fall as freshfilter medium is advanced into the pool, the pressureresponsive switchcan be replaced by a float-operated switch responsive to the level ofpool 46, and the motor 34 which advances the conveyor can be activatedby this floatoperated switch. Other modifications that can be madewithout departing from the scope of the invention as defined in theappended claims will be apparent to those skilled in the art.

We claim:

1. In a filter of the type in which a pool of contaminated liquid to befiltered is formed on a filter medium which is in strip form and issupported on a liquid permeable conveyor that periodically advances thefilter medium to supply fresh medium from a source thereof, theunderside of the filter medium is exposed to a sealed compartment andvacuum pump means is connected to said compartment to reduce thepressure therein and thereby promote filtration, the improvement whichcomprises a transverse partition in said compartment which at its top isin sealing engagement with the underside of said conveyor to formseparate vacuum chambers in said compartment comprising a first vacuumchamber adjacent to said source of filter medium and communicating withthe portion of said conveyor supporting the filter medium entering saidpool and a second vacuum chamber connected to said vacuum pump means andremote from said source of filter medium, conduit means connecting saidfirst chamber above the liquid level therein with said second chamberand flow control means operatively associated with said conduit meansfor maintaining said first chamber at a predetermined and adjustablehigher pressure than said second chamber to reduce the liquid flow ratethrough the portion of the filter medium initially contacting said poolof liquid.

2. A filter according to claim 1 including a conduit effectivelyconnected to said first chamber and having an end open to the atmosphereand valve means in said conduit for adjustably regulating flow of airinto said first chamber.

3. A filter as defined in claim 2 including separate valve means forregulating flow of air into said first chamber and for regulating flowof air between said two chambers.

4. A filter as defined in claim 1 wherein said conduit means includes afirst conduit connected to said first chamber and havingan end open tothe atmosphere and a second conduit connecting said second chamber withsaid first conduit at a point between the open end of said first conduitand said first chamber and said flow control means includes a valve insaid first conduit between its open end and its point of connection tosaid second conduit for regulating air flow to said first chamber and avalve in said second conduit for regulating air flow between said twochambers.

5. A filter having side walls, a liquid permeable endless conveyor,means supporting said conveyor between said side walls, a strip offilter medium mounted on and movable with the top course of saidconveyor and cooperating with said side walls to form a pool of liquidto be filtered, means for feeding liquid to be filtered to said pool,means for periodically moving said conveyor to move a fresh portion ofsaid strip of filter medium into said pool, an evacuatedcompartment'underlying the top course of said conveyor and adapted toreceive filtered liquid passing through said filter medium, a partitionin said compartment which is in sealing engagement at its top with theunderside of sa d conveyor to form separate vacuum chambers in saidcompartment comprising a first vacuum chamber underlying the portion ofsaid pool into which said filter medium is fed and a second vacuumchamber underlying the remainder of said pool, means for recirculatingto said feeding means filtered liquid from said first chamber, vacuumpump means for evacuating said second chamber, a conduit external tosaid compartment connecting said first and second chambers and valvemeans in said conduit adjustable to regulate flow of air from said firstchamber to said second chamber to maintain said first chamber at aselectively higher pressure than said second chamber and thereby reducethe liquid flow rate through the portion of said filter medium initiallycontacting said pool.

6. A filter as defined in claim 5 including a conduit efiectivelyconnected to said first chamber and having an end open to the atmosphereand valve means in said conduit for adjustably regulating flow of airinto said first chamber.

1. In a filter of the type in which a pool of contaminated liquid to befiltered is formed on a filter medium which is in strip form and issupported on a liquid permeable conveyor that periodically advances thefilter medium to supply fresh medium from a source thereof, theunderside of the filter medium is exposed to a sealed compartment andvacuum pump means is connected to said compartment to reduce thepressure therein and thereby promote filtration, the improvement whichcomprises a transverse partition in said compartment which at its top isin sealing engagement with the underside of said conveyor to formseparate vacuum chambers in said compartment comprising a first vacuumchamber adjacent to said source of filter medium and communicating withthe portion of said conveyor supporting the filter medium entering saidpool and a second vacuum chamber connected to said vacuum pump means andremote from said source of filter medium, conduit means connecting saidfirst chamber above the liquid level therein with said second chamberand flow control means operatively associated with said conduit meansfor maintaining said first chamber at a predetermined and adjustablehigher pressure than said second chamber to reduce the liquid flow ratethrough the portion of the filter medium initially contacting said poolof liquid.
 2. A filter according to claim 1 including a conduiteffectively connected to said first chamber and having an end open tothe atmosphere and valve means in said conduit for adjustably regulatingflow of air into said first chamber.
 3. A filter as defined in claim 2including separate valve means for regulating flow of air into saidfirst chamber and for regulating flow of air between said two chambers.4. A filter as defined in claim 1 wherein said conduit means includes afirst conduit connected to said first chamber and having an end open tothe atmosphere and a second conduit connecting said second chamber withsaid first conduit at a point between the open end of said first conduitand said first chamber and said flow control means includes a valve insaid first conduit between its open end and its point of connection tosaid second conduit for regulating air flow to said first chamber and avalve in said second conduit for regulating air flow between said twochambers.
 5. A filter having side walls, a liquid permeable endlessconveyor, means supporting said conveyor between said side walls, astrip of filter medium mounted on and movable with the top course ofsaid conveyor and cooperating with said side walls to form a pool ofliquid to be filtered, means for feeding liquid to be filtered to saidpool, means for periodically moving said conveyor to move a freshportion of said strip of filter medium into said pool, an evacuatedcompartment underlying the top course of said conveyor and adapted toreceive filtered liquid passing through said filter medium, a partitionin said compartment which is in sealing engagement at its top with theunderside of said conveyor to form separate vacuum chambers in saidcompartment comprising a first vacuum chamber underlying the portion ofsaid pool into which said filter medium is fed and a second vacuumchamber underlying the remainder of said pool, means for recirculatingto said feeding means filtered liquid from said first chamber, vacuumpump means for evacuating said second chamber, a conduit external tosaid compartment connecting saiD first and second chambers and valvemeans in said conduit adjustable to regulate flow of air from said firstchamber to said second chamber to maintain said first chamber at aselectively higher pressure than said second chamber and thereby reducethe liquid flow rate through the portion of said filter medium initiallycontacting said pool.
 6. A filter as defined in claim 5 including aconduit effectively connected to said first chamber and having an endopen to the atmosphere and valve means in said conduit for adjustablyregulating flow of air into said first chamber.